Field of the Disclosure
The present disclosure relates to high yield liquid-full catalytic hydroprocesses for the production of middle distillate fuel with reduced sulfur and/or nitrogen content and improved cold flow properties.
Description of Related Art
Global demand for diesel, particularly for low-sulfur-middle diesel (LSD) and more particularly for ultra-low-sulfur-diesel (ULSD) has risen quickly with increased growth of transportation fuels and a decrease in the use of fuel oil. Regulations for transportation fuels have been established to substantially lower the sulfur levels in diesel fuels. There are other pending rules calling to reduce the sulfur content in off-road diesel as well. Thus, there is a growing need for improved diesel products, including LSD and ULSD. Hydroprocessing (or hydrotreating), such as hydrodesulfurization and hydrodenitrogenation, have been used to remove sulfur and nitrogen, respectively from hydrocarbon feeds.
Moreover, in cold weather climates there is a need for diesel fuels with improved cold flow properties, such as improved cloud point, pour point, and cold filter plugging point. Such improved cold flow properties can be obtained by dewaxing techniques.
Conventional three-phase hydroprocessing units used for hydrotreating and high pressure hydrocracking, commonly known as trickle bed reactors, require hydrogen from a vapor phase to be transferred into liquid phase where it is available to react with a hydrocarbon feed at the surface of the catalyst. These units are expensive, require large quantities of hydrogen, much of which must be recycled through expensive hydrogen compressors, and result in significant coke formation on the catalyst surface and catalyst deactivation.
Alternative hydroprocessing approaches include hydrotreating and hydrocracking in a once-through flow scheme as proposed by Thakkar et al. in “LCO Upgrading A Novel Approach for Greater Value and Improved Returns” AM, 05-53, NPRA, (2005). Thakkar et al. disclose upgrading a light cycle oil (LCO) into a mixture of liquefied petroleum gas (LPG), gasoline and diesel products. Thakkar et al. disclose producing a low sulfur content diesel (ULSD) product. However, Thakkar et al. use traditional trickle bed reactors, which require large quantities of hydrogen and large process equipment such as a large gas compressor for hydrogen gas circulation. Significant amounts of light gas and naphtha are produced in the disclosed hydrocracking process. The diesel product accounts for only about 50%, or less, of the total liquid product using LCO feed.
Ackerson, in U.S. Pat. No. 6,123,835, the subject matter of which is herein incorporated by reference, discloses a liquid-full, two-phase hydroprocessing system which eliminates the need to circulate hydrogen through the catalyst. In the liquid-full, two-phase hydroprocessing system, a solvent (or a recycled portion of hydroprocessed liquid effluent) acts as diluent and is mixed with a hydrocarbon feed. Hydrogen is dissolved in the feed/diluent mixture to provide hydrogen in the liquid phase. All of the hydrogen required in the hydroprocessing reaction is available in solution. Thus, no additional hydrogen is required and hydrogen recirculation is avoided and trickle bed operation of the reactor is avoided.
US Patent Application Publication Number 2012/0004477 (US '477) discloses that hydrocarbon feeds can be hydrotreated in a continuous gas phase environment to reduce the sulfur and nitrogen content, and then dewaxed in a liquid-continuous reactor. US '477 discloses that the liquid-continuous reactor can advantageously be operated in a manner that avoids the need for a hydrogen recycle loop. The disclosed method for making diesel fuel product includes contacting a feedstock with a hydrotreating catalyst under effective hydrotreating conditions in a hydrotreatment reactor that includes a continuous gas phase to make a hydrotreated effluent; separating the hydrotreated effluent into at least a hydrotreated liquid product and a gas-phase product (the gas-phase product can include H2, H2S, and NH3) to produce a hydrotreated dewaxing input stream, and contacting the hydrotreated dewaxing input stream with a dewaxing catalyst under effective catalytic dewaxing conditions in a liquid-continuous reactor to form a dewaxed effluent with a cold flow property that is at least about 5° C. less than a corresponding cold flow property of the feedstock. The gas-phase product can be used to provide recycled hydrogen for the hydrotreatment stage and/or a portion mixed with the hydrotreated effluent to form the hydrotreated dewaxing input stream.
US Patent Application Publication Number 2010/0176027 (US '027) discloses an integrated process for producing diesel fuel from feedstocks, including diesel fuel production under sour conditions. The ability to process feedstocks under higher sulfur and/or nitrogen conditions allows for reduced cost processing and increases the flexibility in selecting a suitable feedstock. Moreover, in a disclosed embodiment, product from a hydrotreatment stage is directly cascaded into a catalytic dewaxing reaction zone. No separation is required between the hydrotreatment and catalytic dewaxing stages. Specific catalysts that are more tolerant of contaminants, such as sulfur and nitrogen, compared to conventional dewaxing catalysts are disclosed.
Although substantial improvements have been made in the arts of hydrotreating and dewaxing diesel fuel, the search continues for more robust, economical processes to produce LSD and ULSD with improved cold flow properties.